Mono(2-ethylhexyl)phthalate (MEHP) is both a male and female reproductive toxicant as determined in the NTP Reproductive Assessment by Continuous Breeding protocol. In the male, MEHP has been shown in vivo and in vitro to be a Sertoli cell (SC) toxicant. In vitro MEHP inhibited FSH-stimulated cAMP accumulation in cultured SCs. This inhibition occurred after a 6 hr preincubation period, with maximal inhibition (50%) by 24 hrs. Half-maximal inhibition is seen at 12-15 (mu)M MEHP. Since MEHP is also a female reproductive toxicant, and granulosa cells are thought to be the female counterpart to SCs, we examined the effect of MEHP on FSH-stimulated cAMP accumulation in cultured granulosa cells (GCs). GCs are harvested by ovarian puncture of DES-primed immature (19-22 d) F-344 rats and 300,000 viable cells were incubated in plastic tubes for up to four days. FSH, forskolin, and isoproterenol were shown to stimulate cAMP accumulation. MEHP inhibited FSH-stimulated cAMP accumulation in a dose- and time-dependent manner. Significant inhibition (30-50%) of GC cAMP accumulation occurred with 200 (mu)M MEHP after a 15 hr exposure, with maximal inhibition at 30 hrs. MEHP also inhibits progesterone production. Thus, the action of MEHP on GCs appears to be limited to an effect to decrease FSH-stimulated cAMP production. This decrease in cAMP levels then results in decreased progesterone production which may be an important part of the female reproductive toxicity of MEHP.